As well known in the art, in order to manufacture a semiconductor device, an electronic device, a photoelectronic device, a magnetic device, a display device, a microelectromechanical device and the like, a process for forming a micro pattern on a substrate is required to be performed. As a representative technique for forming the micro pattern on the substrate, there is a photolithographic method for forming a micro pattern by using light.
According to the photolithographic method, a polymer material (such as a photoresist and the like) having an optical sensitivity is coated on a substrate on which a material to be patterned is laminated or deposited and, then, the polymer material is exposed to a light through an exposure process which uses a reticle designed with a certain target patterning. Then, the exposed polymer material is removed by a developing process so that a pattern mask or an etching mask having a target patterning may be formed on the material to be patterned. Thereafter, by performing an etching process with the pattern mask, the material laminated on the substrate can be patterned with a desired pattern.
Meanwhile, in the above-described photolithographic method, a circuit line-width or a pattern line-width is dependent on a bandwidth of the light used in the exposure process. Therefore, it is very difficult to form a hyperfine pattern having a line-width smaller than or equal to, e.g., 100 nm, on the substrate by using a conventional photolithographic method.
Further, since such a conventional photolithographic method requires various steps (such as a substrate cleaning process, a substrate surface treatment, a photosensitive polymer coating process, a low temperature heat treatment, an exposure, a developing, a cleaning, a high temperature heat treatment and the like), the method itself becomes complex and a considerable processing time is needed. Besides, high-priced processing equipments are required, thereby increasing a manufacturing cost and deteriorating a productivity.
In order to overcome limits of the conventional photolithographic method, non-conventional lithographic methods are being suggested.
One of the non-conventional lithographic methods is a nano-imprint lithographic method for transferring a pattern of a hard mold to a polymer thin film pattern of a substrate by preparing the hard mold made of silicon (Si) on which a desired pattern is formed and the substrate whose surface is coated with a thermoplastic polymer thin film, facing the hard mold with the substrate, performing a compression on the hard mold and the substrate under a condition of a high temperature and a high pressure by using a plate press, and separating the compressed-mold from the substrate.
Such a nano-imprint lithographic method has an advantage that it is easy to form a hyperfine pattern because the hard mold made of silicon and the like is used. In fact, according to a research, a minimum size of the pattern has been known as about 7 nm.
However, the conventional nano-imprint lithographic method has drawbacks to be described as follows. Above all, it is difficult to separate the mold from the substrate after the compression under the high temperature and the high pressure is terminated. Further, the high pressure during the compression results in a possibility of damaging the mold and the substrate. Moreover, since the patterning is performed by using a fluidity of the high temperatured polymer material, a considerable time is required to complete the patterning described above, especially, in case of a large sized pattern so that a processing time increases.
Other examples of the non-conventional lithographic methods include a micro-contact printing (μCP), a micro-molding in capillaries (MIMIC), a micro-transfer molding (μTM), a soft molding, a capillary force lithography (CFL) and the like. In such methods, it is common that a kind of polymer elastomer of polydimethylsiloxane (PDMS) is used as a mold.
Since the PDMS mold used in the conventional nano-imprint lithographic methods is an elastomer, it is easy for the PDMS mold to be in conformal contact with a surface of a substrate to be patterned. Further, since the PDMS mold has a lower surface energy, an adhesive force of the PDMS mold to a surface of other materials is low enough to enable the PDMS mold to be easily separated from the surface of the substrate after the patterning is terminated. Additionally, its high gas permeability due to a three-dimensional net-work structure results in an easy absorption of a solvent thereinto.
Meanwhile, since the PDMS mold is an elastomer having a low mechanical strength, the PDMS mold may be easily deformed so that the PDMS mold may not be used to form a micro pattern with a pattern size smaller than or equal to, e.g., about 500 μm and highly dependent on an aspect ratio of the pattern to be formed. In addition, the PDMS mold is swollen and deformed by a general organic solvent such as toluene and the like so that a selection of the polymer and the solvent to be used in the patterning may be restricted.